noun
dip; magnetic dip; inclination
Technical term in geomagnetism: the angle a compass needle makes with the horizontal plane. Also read ふくかく, though ふっかく is more common.
磁気伏角は場所によって異なる。
Magnetic dip varies depending on the location.
この地域では伏角が約45度である。
In this region, the dip is about 45 degrees.
偏角 is magnetic declination (horizontal angle between magnetic north and true north), while 伏角 is magnetic dip (vertical angle).
Compound of 伏 (ふく, 'bend down, incline') and 角 (かく, 'angle'). The reading ふっかく is a common gemination of the first character's reading.